This invention relates to slip prevention of power rollers of a toroidal continuously variable transmission.
U.S. Pat. No. 5,542,890 discloses a toroidal continuously variable transmission for vehicles (referred to hereafter as a toroidal CVT) wherein power rollers are gripped between an input disk and output disk facing each other. In this toroidal CVT, the rotation of the input disk is transmitted to the output disk via the power rollers, and the ratio of the rotation speeds of the input disk and output disk, i.e. the speed ratio of the transmission, varies continuously according to the gyration angle variation of the power rollers. Oil is supplied to the surfaces of these disks and power rollers, and torque is transmitted by the shear drag of the oil between the contact parts of the power rollers and disks.
In vehicles in which the rotation output of the engine is not input into the toroidal CVT in a neutral range, i.e., vehicles provided with a clutch between the engine and the toroidal CVT, the power rollers and disks do not rotate in the neutral range. Therefore, when vehicles start at low temperature and the selector lever of the vehicles is changed over to a drive range from the neutral range, a torque will act on the low temperature oil. At such low temperatures, the shear drag of the oil is not fully obtained, so immediately after the selector lever is changed over to the drive range from the neutral range, or when the accelerator pedal is depressed to accelerate the vehicle in the drive range, the power rollers may slip. This slip of the power rollers has a undesirable effect on speed ratio control of the transmission.
It is therefore an object of this invention to prevent slip of the power rollers at a low oil temperature.
In order to achieve the above object, this invention provides a slip preventing device of a power roller of a toroidal continuously variable transmission which varies an output rotation of an engine of a vehicle under an arbitrary speed ratio. The transmission comprises two disks disposed coaxially and the power roller is in contact with the two disks. Surfaces of the two disks and the power roller are provided with oil. The device comprises a sensor which detects a temperature of the oil, a mechanism which suppresses an output torque of the engine, and a microprocessor programmed to control the suppressing mechanism to suppress the output torque of the engine when the temperature of the oil is lower than a predetermined temperature.
This invention also provides a slip preventing method of a power roller of a toroidal continuously variable transmission which varies an output rotation of an engine of a vehicle under an arbitrary speed ratio. The transmission comprises two disks disposed coaxially and the power roller is in contact with the two disks. Surfaces of the two disks and the power roller are provided with oil. The method comprising detecting a temperature of the oil, and suppressing an output torque of the engine when the temperature of the oil is lower than a predetermined temperature.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.